The present invention relates to nuclear reactors having a suspended vessel and applies more particularly to a reactor of the fast neutron type in which the core or active part of the reactor is located in the vessel and immersed in a suitable volume of a circulating liquid metal which ensures its cooling by the extraction of calories given off by nuclear fission in the fuel assemblies forming the core.
The general concept of a "reactor block" of the above type is completely standard in the art, more particularly in the so-called integrated design where the vessel containing the liquid metal which has a generally cylindrical configuration with a substantially spherical base is open in the upper part and is suspended with its vertical axis below an upper protective plate which seals the vessel and ensures the protection of the external environment. The plate rests by its periphery on a bearing surface provided in a generally concrete thick-walled caisson which defines a cavity which receives the vessel. In this solution the plate also supports a system of rotary plugs disposed vertically relative to the core and carrying means permitting access to be obtained to the latter in order to ensure the inspection and handling of the fuel assemblies, a system of heat exchangers and circulating pumps distributed around the core and after traversing the plate immersed in the volume of liquid metal contained in the vessel. On leaving the core the hot liquid metal passes through the exchangers where it gives off the calories taken up and once cooled is taken up again in the vessel by pumps which return it under an adequate pressure to below the core for a further passage through the latter.
It is readily apparent that in a design of this type a critical part of the installation is the area in which the upper part of the cylindrical ferrule of the vessel is anchored in the plate. In particular this area must be protected relative to the thermal flux created by liquid metal aerosols from the vessel and also relative to too high temperature gradients and too sudden variations in said gradients which are liable to occur in operation or on stopping the reactor.
The invention relates more particularly to providing against the inner wall of the vessel in the vicinity of the area in which it is fixed to the plate of a continuous heat insulating structure which effectively satisfies the above requirements, said structure being designed in such a way that it can be applied to the wall of the vessel without being fixed thereto by welding or other connecting means liable to destroy the mechanical integrity of the vessel and its strength.